You can buy some electrical cleaner, spray it on, and then lightly scrape off the green stuff with a flat head or anything else you can find. Make sure to get rid off the green stuff from both the connector and where the connector connects. Once youre done make sure you let the connectors completely dry and then feel free to put electric grease on them for better conductivity and to prevent future corrosion. Oh and make sure you do all of this with the battery disconnected.
P.S. Cleaning one of my injectors like this solved my problem when i was running on only 5 cylinders because the connector was too dirty.